Carbon-coated Nanoparticles Research Articles

Synthesis of carbon-coated iron nanoparticles by detonation technique

Carbon-coated iron nanoparticles were synthesized by detonating a mixture of ferrocene, naphthalene and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in an explosion vessel under low vacuum conditions (8.1 kPa). The RDX functioned as an energy source for the decomposition of ferrocene and naphthalene. The carbon-coated iron nanoparticles were formed as soot-like deposits on the inner surface of the reactor, which were characterized by XRD, TEM, HRTEM, Raman spectroscopy and vibrating sample magnetometer. And a portion of the detonation soot was treated with hydrochloric acid. The product was carbon-coated nanoparticles in perfect core–shell structures with graphitic shells and bcc-Fe cores. The detonation technique offers an energy-saving route to the synthesis of carbon-coated nanomaterials.

A hollow sphere secondary structure of LiFePO4 nanoparticles

We report on the evolution of a hollow sphere secondary structure of spherical nanoparticles by a solubilization-reprecipitation mechanism based on the difference of solubility products (K(sp)) of two different precipitates. Carbon-coated nanoparticles of olivine structure LiFePO(4) served as the primary nano-blocks to build the secondary nano-architecture.

Chloroethene dehalogenation with ultrasonically produced air-stable nano iron

Zerovalent iron (ZVI) has been demonstrated to be suitable for the dehalogenation of environmental pollutants such as chloroethenes. The construction of ZVI reactive barriers by conventional engineering measures is expensive and limited to shallow aquifers. The use of nanosized ZVI particles opens new opportunities to construct ZVI barriers with less invasive techniques. However, nanosized particles of pure ZVI are pyrophoric and react spontaneously with atmospheric oxygen. In this study, nanosized air-stable ZVI particles were produced by applying ultrasound to a solution of Fe(CO) 5 in edible oil. The resulting iron nanoparticles were dispersed in a carbon matrix, and coated with a non-crystalline carbon layer of approx. 2.5 nm. Although, these nanoparticles are non-pyrophoric and stable in air, dechlorination of tetrachloroethene was demonstrated in synthetic aqueous medium and in polluted groundwater. Additionally, hydrogen was formed. Due to the larger surface area, significantly higher mass-normalized reaction rates of the novel carbon-coated nanoparticles were obtained as compared to conventional bulk ZVI material. Surface normalized pseudo-first-order-reaction rates of k SA = 3.49 × 10 −3 L h −1 m −2 and 2.33 × 10 −2 L h −1 m −2 were calculated for the nano-ZVI and the bulk ZVI, respectively. Dechlorination reaction products of the novel nano-ZVI were trichloroethene, cis-dichloroethene, vinyl chloride, ethene, and ethane.

Synthesis and thermal stability of carbon-supported Ru–Ni core-and-shell nanoparticles

Binary nanoparticles of Ru–Ni supported on a carbon nanolayer and carbon-coated Ru–Ni core-and-shell nanoparticles were synthesized in a single step spray-pyrolysis process. A precursor containing ruthenium chloride and nickel chloride solution mixture was used to deposit Ru–Ni nanoparticles on a carbon nanolayer generated from hexane. Carbon-coated nanoparticles were produced by using ruthenium chloride and nickel chloride solution mixed with methanol and hexane as precursor in the spray-pyrolysis process. A carbon layer that was derived from the thermal decomposition of hexane and methanol forms a protective shell around the binary core-and-shell nanoparticles of Ru–Ni. TEM and EDS spectral graphs confirm the presence of carbon layers encapsulating the Ru–Ni nanoparticles. The encapsulating carbon layers are effective in reducing agglomeration of binary nanoparticles in the spray-pyrolysis process. The carbon-coated binary nanoparticles were subjected to heat treatment at temperatures up to 800 °C, the size and morphology of the nanoparticles before and after heat treatment were compared to examine the thermal stability of the nanoparticles. It was observed that the carbon-coated Ru–Ni nanoparticles exhibit unique thermal stability. EDS, SEM, and TEM data revealed that the morphology of the nanoparticles did not change during the heat treatment.

The Study of Carbon-Coated V2O5 Nanoparticles as a Potential Cathodic Material for Li Rechargeable Batteries

Carbon-coated nanoparticles are good candidates as cathodic materials for rechargeable Li batteries. These nanoparticles were prepared by burning off carbon-coated nanoparticles in air (around ). The nanoparticles were prepared by a simple, single-stage reaction under autogenic pressure. Variations in the conditions of the burning process determine the properties of the carbon coating (e.g., thickness, weight % of carbon). Several types of electrodes were investigated. These included composite electrodes comprising different batches of , additional carbon particles and PVdF binder, composite electrodes comprising micrometric size, commercial as the active mass, and electrodes in which the or micronic size particles were embedded in aluminum foils without using any carbon additive or binder. The electrochemical response in terms of capacity, cyclability, and rates (up to 5C) at different potential ranges (narrow and wide domains, vs ) was investigated in and in ethylene carbonate/dimethyl carbonate solutions by standard electrochemical techniques, including chronopotentiometry, cyclic voltammetry, and impedance spectroscopy. The behavior of the electrodes (nanoparticles) was compared to that of electrodes comprising micronic size particles. In general, electrodes demonstrated a higher capacity, much better rate capability, and very good stability upon cycling and aging at elevated temperatures compared to electrodes comprising microparticles of . In situ and ex situ atomic force microscopy imaging was used for the morphological analysis of these electrodes.

Fabrication of carbon-coated cobalt nanoparticles by the catalytic method

A mass of carbon-coated cobalt nanoparticles were successfully synthesized by chemical vapor deposition of methane over Co/Al catalyst at 650 °C. The phases found in the as-prepared carbon-coated nanoparticles were fcc-Co. The diameter of these nanoparticles with 2–10 nm carbon coating shell was in the range of 5–80 nm. However, it is well-known that the Co nanoparticles are suitable for carbon nanotube synthesis, such as Co/Al 2O 3 and Co/SiO 2 catalysts. Here, we speculated that the formation mechanism of carbon-coated cobalt nanoparticles might due to that the formation of carbon nanotubes was inhibited by the catalyst supporter of Al. Compared with Al 2O 3 and SiO 2, Al possesses very low melting point (660 °C), very high diffusion coefficient and thermal conductivity, thus the isotropic precipitation of carbon species on the surface of cobalt particles took place, favoring the formation of carbon-coated Co nanoparticles.

Activation volume and magnetization reversal of nanoparticle films composed of magnetically isolated Fe–Pt nanoparticles

We report on activation volume and magnetization reversal of Fe–Pt nanoparticle films. In order to diminish coalescence and sintering during high-temperature annealing above 700K, carbon overcoats are deposited on Fe–Pt nanoparticle-films. TEM observations reveal that grains in the Fe–Pt nanoparticle-films are kept to be 5–6nm in size even after annealing at 873K; the particle size is close to the crystalline size estimated by Scherrer’s formula as 5nm from x-ray diffraction. In-plane coercivity at room temperature is 2.5kOe; the activation volume (1.16×10−19cm3) at around the coercivity is almost equal to the physical volume of the particles observed by TEM, suggesting that the nanoparticles are magnetically isolated and the magnetization reversal is based on rotation mode in the carbon-coated nanoparticle films.

A Direct Route toward Assembly of Nanoparticle−Carbon Nanotube Composite Materials

The preparation of nanocomposite materials from carbon nanotubes (CNTs) and metal or metal oxide nanoparticles has important implications to the development of advanced catalytic and sensory materials. This paper reports findings of an investigation of the preparation of nanoparticle-coated carbon nanotube composite materials. Our approach involves molecularly mediated assembly of monolayer-capped nanoparticles on multiwalled CNTs via a combination of hydrophobic and hydrogen-bonding interactions between the capping/mediating shell and the CNT surface. The advantage of this route is that it does not require tedious surface modification of CNTs. We have demonstrated its simplicity and effectiveness for assembling alkanethiolate-capped gold nanoparticles of 2-5 nm core sizes onto CNTs with controllable coverage and spatially isolated character. The loading and distribution of the nanoparticles on CNTs depend on the relative concentrations of gold nanoparticles, CNTs, and mediating or linking agents. The composite nanomaterials can be dispersed in organic solvent, and the capping/linking shells can be removed by thermal treatment to produce controllable nanocrystals on the CNT surfaces. The nanocomposite materials are characterized using transmission electron microscopy and Fourier transform infrared spectroscopy techniques. The results will be discussed in terms of developing advanced catalytic and sensory nanomaterials.

Microstructure and Magnetic Properties of Fe(C) and Fe(O) Nanoparticles

AbstractTwo types of iron (Fe) nanoparticles, carbon-coated Fe nanoparticles (Fe(C)) and pure α-Fe nanoparticles that coated with oxide layers (Fe(O)), have been successfully synthesized using modified graphite arc-discharge method. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HREM) and electron diffraction (SAED) analysis have been used to characterize these distinct structural morphologies. It is indicated that those two Fe nanoparticles have an average grain size of 15-20nm. The presence of carbon encapsulated α-Fe, γ-Fe and Fe3C phases are clearly identified by X-ray diffraction and SAED patterns in those Fe(C) particles. However, the evidence of pure α-Fe nanocrystal coated with oxide layer is also revealed by HR-TEM images and SAED patterns in these Fe(O) particles.Mössbauer spectra and hyperfine magnetic fields at room temperature for the assemblies of Fe(C) and Fe(O) nanoparticles further confirm their distinct nanophases that detected by XRD analysis and HRTEM observation. Specially, the assemblies of Fe(O) nanoparticles exhibit ferromagnetic properties at room temperature due to the stronger interparticle interaction and bigger magnetocrystalline anisotropy effects among these Fe(O) nanoparticles. Moreover, modified superparamagnetic relaxation is observed in the assemblies of Fe(C) nanoparticles, which is attributed to the nanocrystalline nature of the carbon-coated nanoparticles.

Carbon Coated Nanoparticle Composites Synthesized in an RF Plasma Torch

ABSTRACTFeCo alloy nanoparticles are synthesized in an RF plasma torch reactor and characterized using X-ray powder diffraction (XRD) and transmission electron microscopy (XRD). Bare, uncoated particles exhibit a chain-like agglomeration morphology marked by large ring- and bridge-like structures surrounding open voids. Acetylene was used to generate large numbers of carbon-coated nanoparticles similar to those produced in carbon arc reactors. Conventional TEM of this powder revealed numerous particles below 50 nm in diameter embedded in a carbonaceous matrix. These results establish RF plasma torch processing as a well-characterized, scalable alternative to carbon arc synthesis of encapsulated nanoparticles.

Formation of Nanoparticles in A Carbon Arc

ABSTRACTDetails of the carbon-coated nanoparticle growth mechanism are revealed by a comparison of product morphology and reactor parameters. Carbon-coated metal or metal carbide clusters nucleate in the gas phase, grow to characteristic sizes, and deposit on surfaces within the reactor. The surface temperature determines the crystallinity of the nanoparticles and the surrounding carbon. Tungsten carbide nanoparticles show that the carbon coating arises due to phase segregation when the nanoparticle has a lower melting point than that of graphite.

Morphology of Nanoparticles and Fullerene Blacks Produced in A Carbon Arc

ABSTRACTUsing X-ray powder diffraction and transmission electron microscopy we examine the morphology and crystallographic structure of carbon-coated nanoparticles produced in a modified Huffman-Kratschmer carbon arc process. Graphite rods containing Ho were consumed in the arc and soots sampled from both the reactor walls and the inner core of the cathode deposit are compared. The inner core soot displays increased crystallinity and less amorphous carbon than wall-deposited soot, and nanoparticles in the inner core have more graphitic layers in the encapsulating shells, more gaps between the carbon coating and the core, and exhibit a greater degree of facetting than particles harvested from the reactor walls. These differences are interpreted as manifestations of the high temperature post-formation environment of the inner core of the cathode deposit.